The melanocortin receptors (MCRs) are G-Protein Coupled Receptors (GPCRs) that modulate and control many critical physiological processes in animals including pigmentation, response to stress, feeding behavior, energy balance, sexual function and behavior, inflammatory response, cardiovascular function, immune response, pain and others. They also are involved in many of our most common degenerative diseases including adrenal dysfunction, obesity, anorexia, pigmentary disorders, sexual dysfunction, prolonged and neuropathic pain, inflammatory disorders, cardiovascular disease and others. Yet there are few compounds that have been developed and are pharmaceuticals in use for treatment of these diseases which are our most common and difficult to treat diseases. This grant is dedicated to developing more potent, receptor selective, and specific and most efficacious ligands for the melancortin 1(MCI), melanocortin 3 (MC3), melanocortin 4 (MC4), and melanocortin 5 (MC5) receptors. These novel ligands, which are biological stable and available for in vivo applications, will be useful for studying the pharmacology, physiology and medical applications of melanotropin ligands. The specific aims we will pursue include: 1) development and use of novel protein/peptide topologies and scaffolds, in conjunction with novel constrained amino acids, to design and synthesize novel orthosteric, allosteric, and biased melanotropin peptides and peptide mimetics with enhanced stability, bioavailability, selectivity and potency for the melanocortin receptors; 2a) to examine binding affinities, cyclic AMP production, efficacies, Ca+2 assays and assays for ?- arrestin. The novel ligands for the hMC1R, hMC3R, hMC4R and hMC5R receptors will be examined with special attention to the development of biased ligands; and 2b) use of novel selective ligands, especially those with biased activity, to explore novel physiological functions that can lead to novel drugs with our collaborators.